...

filter.hs

@@ -4,11 +4,14 @@ import Text.Pandoc.JSON
 import qualified Data.Text.IO as TIO
 import qualified Data.Text as T
 
+file2Block :: FilePath -> IO [Block]
+
+
 doInclude :: Block -> IO Block
-doInclude cb@(CodeBlock (id, classes, namevals) contents) =
+doInclude cb@(Div (id, classes, namevals) contents) =
   case lookup (T.pack "include") namevals of
-       Just f     -> CodeBlock (id, classes, namevals) <$>
-                      TIO.readFile (T.unpack f)
+       Just f     -> Div (id, classes, namevals) <$>
+                      file2Block (T.unpack f)
        Nothing    -> return cb
 doInclude x = return x
 

input.md

@@ -1,5 +1,9 @@
 Here's the pandoc README:
 
+```haskell {include="filter.hs" style="background-color: red"}
+Foo:: Div -> Div
+```
+
 :::{include="filter.hs"}
 :::